Peek Behind the Sneaks: Bringing Depth to the Digital Brush

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If you walk into any gallery and look closely at the oil paintings, you’ll notice something right away — they’re actually three-dimensional works of art rising off the surface of the canvas.  The combination of pigments, the layering of the paint and the organic traces of the brushstrokes all serve to reinforce the vision of the painter, influencing the mood and energy of the artwork.  It’s a key part of what makes a painting like Van Gogh’s The Starry Night feel so vital to the human eye.
It’s also an effect that has eluded most digital painting programs — until now.  As part of the sneaks presentations at MAX 2016, Adobe previewed a technology called Project WetBrush that brings physics-based brush and particle simulation to oil painting on a pressure-sensitive tablet.
“If you look at the way most painting programs simulate a brushstroke, it’s actually a two dimensional stamp of a stroke that gets repeated along a path,” explains Zhili Chen, research scientist with Adobe Research.  That’s an effect that can begin to look repetitive or artificial when applied to an entire painting, and it limits an artist’s potential for expression.
“What we’re doing with WetBrush,” Zhili continues, “is an actual physics simulation of the thousands of bristles in a brush, and the millions of particles of pigment in the paint itself.  That means we can simulate the interaction of each particle of pigment with each individual bristle and model the brush shape, friction and interaction with the surface of the canvas.”
The result for the digital artist is an organic, expressive stroke that responds more naturally to the angle, pressure and length of the brush stroke.  What’s more, since the stroke is based on a physics simulation, rather than a two-dimensional stamp, the finished work can even be 3D printed, maintaining the peaks and valleys of the brushstroke.
 Although the technology behind this type of realistic physics simulation has been understood for sometime, it’s traditionally required the kind of computational power that’s made it impractical for real-time simulation on a tablet.  If the simulation is detailed enough, it could take a whole day to simulate a single brushstroke.
What’s made it possible for WetBrush to work on a tablet now is a combination of improved GPU processing capability in the hardware, alongside some innovative algorithms and a clever hybrid of particle simulation modeling for particles near the brush combined with grid-based simulation for particles on the canvas to speed things up.  It’s an approach several years in the making, developed collaboratively between researchers at Adobe and Ohio State University.  In fact, Zhili started his work on the project as a Ph.D. student at Ohio State and developed it further as an Adobe intern.
“It took a lot of fine tuning to make WetBrush work,” explains Zhili. “To try to model everything at the molecular level, and have it be fast enough to keep up with a brushstroke is a huge challenge.“
Today, in his role as an Adobe research scientist, Zhili hopes to continue to improve WetBrush as well as apply physics-based simulation in new, unexpected ways.  “We want to increase the resolution and detail, to simulate even more bristles and particles and find innovative algorithms that can speed up the process even more,” he notes.  “We’re also looking at other ways we can apply real-time physics to enable the artist to do things like work with realistic metallic paints, or even paint with smoke, fire and animated features.
“Real-time physics simulations like these will be critical not just for drawing programs, but for bringing the world to life in virtual or augmented realities in the future.”
This story is part of a series that will give you a closer look at the people and technology that were showcased as part of Adobe Sneaks. Watch other Sneaks from this year’s MAX here and read other Peek Behind the Sneaks stories here.